Review for Copy Email Folder by RedSnt
Rated 5 out of 5 stars
Wanted to do a simple copy job based on a search result, and to my surprise Thunderbird doesn't support copying search results out of the box. By saving the search results and using this add-on, it was quite easy. A bonus that it also has the option to not make duplicates, which is something Thunderbird's native copy feature doesn't account for.
Only thing that could've made this better was an option to cancel the copy job, but I imagine there might be limitations.
One other thing: Thunderbird's builtin copy feature seem to stop at 9000 exactly, at least that's what I saw yesterday. This addon just keeps on trucking, I doubt there's a limit.
To create your own collections, you must have a Mozilla Add-ons account.